Mapusaurus

Mapusaurus Temporal range: Late Cretaceous, 95 Ma PreЄ Є O S D C P T J K Pg N ↓
Reconstructed skeletons of an adult and a juvenile (left)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	Dinosauria
Order:	Saurischia
Suborder:	Theropoda
Family:	†Carcharodontosauridae
Tribe:	†Giganotosaurini
Genus:	†Mapusaurus Coria & Currie, 2006
Species
†M. roseae Coria & Currie, 2006 (type)

Mapusaurus ("earth lizard") was a giant carnosaurian dinosaur from the early Late Cretaceous (Cenomanian stage) of what is now Argentina.

Description

Size compared to a human, based on the largest fragmentary specimen

It was similar in size to its close relative Giganotosaurus, with the largest known individuals estimated as about 10.2 metres (33 ft) in length and weighing approximately 3 metric tons (3.3 short tons).^[1] The longest individual for which Coria and Currie (2006) provided an estimate is the animal to which femur MCF-PVPH-208.203 belonged; this individual is estimated as 10.2 metres (33 ft) long. Coria and Currie note the presence of isolated bones from at least one longer individual, but do not provide a figure, instead finding the larger bones comparable in size to those from a Giganotosaurus estimated at 12.2 metres (40 ft) in length. Maximum length is thus unknown but greater than 12.2 metres (40 ft). The weight estimate is from another femur (MCF-PVPH-208.234). It was furthermore concluded that the largest remain, a pubic shaft, was 110% the size of the Giganotosaurus holotype. Holtz estimated it at 12.6 metres (41 ft).^[2] In an analysis on the cranial anatomy of carcharodontosaurids, Drew Eddy and Julia Clarke (2011) estimated the size of Mapusaurus at 12.6 metres (41 ft).^[3] this estimate was repeated in a calibrated phylogenetic table in a 2014 analysis by Canale et al.^[4]

Coria and Currie diagnosed Mapusaurus as follows: "Mapusaurus n. gen. is a carcharodontosaurid theropod whose skull differs from Giganotosaurus in having thick, rugose unfused nasals that are narrower anterior to the nasal/maxilla/lacrimal junction; larger extension of the antorbital fossa onto maxilla; smaller maxillary fenestra; wider bar (interfenestral strut) between antorbital and maxillary fenestrae; lower, flatter lacrimal horn; transversely wider prefrontal in relation to lacrimal width; ventrolaterally curving lateral margin of the palpebral; shallow interdental plates; higher position of Meckelian canal; more posteriorly sloping anteroventral margin of dentary. Mapusaurus roseae is unique in that the upper quadratojugal process of jugal splits into two prongs; small anterior mylohyoid foramen positioned above dentary contact with splenial; second and third metacarpals fused; humerus with broad distal end and little separation between condyles; the brevis fossa of the ilium extends deeply into excavation dorsal to ischial peduncle. It also differs from Giganotosaurus in having conical, slightly curving cervical epipophyses that taper distally; axial posterior zygapohyses joined on midline; smaller and less elaborate prespinal lamina on midline of cervicals; remarkably sharp dorsal margin of cervical neural spines; tall, wider neural spines; curved ischiatic shaft; more slender fibula."^[1]

Discovery

Reconstructed skull

Mapusaurus was excavated between 1997 and 2001, by the Argentinian-Canadian Dinosaur Project, from an exposure of the Huincul Formation (Rio Limay Subgroup, Cenomanian) at Canadon de Gato. It was described and named by paleontologists Rodolfo Coria and Phil Currie in 2006.^[1]

The name Mapusaurus is derived from the Mapuche word Mapu, meaning 'of the Land' or 'of the Earth' and the Greek sauros, meaning 'lizard'. The type species, Mapusaurus roseae, is named for both the rose-colored rocks, in which the fossils were found and for Rose Letwin, who sponsored the expeditions which recovered these fossils.

The designated holotype for the genus and type species, Mapusaurus roseae, is an isolated right nasal (MCF-PVPH-108.1, Museo Carmen Funes, Paleontología de Vertebrados, Plaza Huincul, Neuquén). Twelve paratypes have been designated, based on additional isolated skeletal elements. Taken together, the many individual elements recovered from the Mapusaurus bone bed represent most of the skeleton.^[1]

Paleobiology

Artist's impression

The fossil remains of Mapusaurus were discovered in a bone bed containing at least seven individuals of various growth stages.^[5][6] Coria and Currie speculated that this may represent a long term, possibly coincidental accumulation of carcasses (some sort of predator trap) and may provide clues about Mapusaurus behavior.^[1] Other known theropod bone beds include the Allosaurus-dominated Cleveland Lloyd Dinosaur Quarry of Utah, an Albertosaurus bone bed from Alberta and a Daspletosaurus bone bed from Montana.

Mapusaurus bones with pathologies

Paleontologist Rodolfo Coria, of the Museo Carmen Funes, contrary to his published article, repeated in a press-conference earlier suggestions that this congregation of fossil bones may indicate that Mapusaurus hunted in groups and worked together to take down large prey, such as the immense sauropod Argentinosaurus.^[7] If so, this would be the first substantive evidence of gregarious behavior by large theropods other than Tyrannosaurus, although whether they might have hunted in organized packs (as wolves do) or simply attacked in a mob, is unknown. The authors interpreted the depositional environment of the Huincul Formation at the Canadon de Gato locality as a freshwater paleochannel deposit, "laid down by an ephemeral or seasonal stream in a region with arid or semi-arid climate".^[1] This bone bed is especially interesting, in light of the overall scarcity of fossilized bone within the Huincul Formation. An ontogenetic study by Canale et al (2014)^[8] found that Mapusaurus displayed heterochrony, an evolutionary condition in which the animals may retain an ancestral characteristic during one stage of their life but lost it as they developed. In Mapusaurus, the maxillary fenestrae are present in the younger individuals but gradually disappeared as they matured.

Classification

Cladistic analysis carried out by Coria and Currie definitively showed that Mapusaurus is nested within the clade Carcharodontosauridae. The authors noted that the structure of the femur suggests a closer relationship with Giganotosaurus than either taxon shares with Carcharodontosaurus. They created a new monophyletic taxon based on this relationship, the subfamily Giganotosaurinae, defined as all carcharodontosaurids closer to Giganotosaurus and Mapusaurus than to Carcharodontosaurus. They tentatively included the genus Tyrannotitan in this new subfamily, pending publication of more detailed descriptions of the known specimens of that form.^[1]

A skull comparison between two Mapusaurus roseae skulls

The following cladogram after Novas et al., 2013, shows the placement of Acrocanthosaurus within Carcharodontosauridae.^[9]

	Allosaurus Carcharodontosauridae Neovenator Eocarcharia Concavenator Acrocanthosaurus Shaochilong Carcharodontosaurinae Carcharodontosaurus Giganotosaurini Tyrannotitan Mapusaurus Giganotosaurus

Paleoecology

As previously mentioned, the Huincul Formation is thought to represent an arid environment with ephemeral or seasonal streams. The age of this formation is estimated at 97-94 mya. The dinosaur record is considered sparse here. Mapusaurus shared its environment with sauropods Argentinosaurus (one of the largest sauropods, if not the largest), and Cathartesaura. Abelisauroid theropods Skorpiovenator and Ilokelesia also lived in the region.^[10]

References

1. Coria, R. A.; Currie, P. J. (2006). "A new carcharodontosaurid (Dinosauria, Theropoda) from the Upper Cretaceous of Argentina". Geodiversitas. 28 (1): 71–118. ISSN 1280-9659.
2. Holtz, Thomas R. Jr. (2012) Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages, Winter 2011 Appendix.
3. "Eddy DR, Clarke JA (2011) New Information on the Cranial Anatomy of Acrocanthosaurus atokensis and Its Implications for the Phylogeny of Allosauroidea (Dinosauria: Theropoda). PLoS ONE 6(3): e17932. doi:10.1371/journal.pone.0017932".
4. "Canale JI, Novas FE, Salgado L, Coria RA. 2014. Cranial ontogenetic variation in Mapusaurus rosae (Dinosauria: Theropoda) and the probable role of heterocrony in carcharodontosaurid evolution. Palaeontol Z doi: 10.1007/s12542-014-0251-3".
5. Canale JI, Novas FE, Salgado L, Coria RA. 2014. Cranial ontogenetic variation in Mapusaurus rosae (Dinosauria: Theropoda) and the probable role of heterocrony in carcharodontosaurid evolution. Palaeontol Z doi: 10.1007/s12542-014-0251-3
6. Eddy DR, Clarke JA (2011) New Information on the Cranial Anatomy of Acrocanthosaurus atokensis and Its Implications for the Phylogeny of Allosauroidea (Dinosauria: Theropoda). PLoS ONE 6(3): e17932. doi:10.1371/journal.pone.0017932
7. Associated Press (2006). Details Revealed About Huge Dinosaurs. ABC News US.
8. Canale, Juan (September 24, 2014). "Cranial ontogenetic variation in Mapusaurus roseae (Dinosauria: Theropoda) and the probable role of heterochrony in carcharodontosaurid evolution". Palaeontol Z.
9. Novas, Fernando E. (2013). "Evolution of the carnivorous dinosaurs during the Cretaceous: The evidence from Patagonia". Cretaceous Research. 45: 174–215. doi:10.1016/j.cretres.2013.04.001.
10. Sánchez, Maria Lidia; Heredia, Susana & Calvo, Jorge O. (2006): Paleoambientes sedimentarios del Cretácico Superior de la Formación Plottier (Grupo Neuquén), Departamento Confluencia, Neuquén [Sedimentary paleoenvironments in the Upper Cretaceous Plottier Formation (Neuquen Group), Confluencia, Neuquén]. Revista de la Asociación Geológica Argentina 61(1): 3-18. PDF fulltext

External links

• Meat-Eating Dinosaur Was Bigger Than T. Rex. National Geographic News.
• "What were the longest/heaviest predatory dinosaurs?". Mike Taylor. The Dinosaur FAQ. August 27, 2002. (Named as Unnamed Argentinian Carcharodontosaurine)
• "[And the Largest Theropod is... http://dml.cmnh.org/2003Jul/msg00355.html]". The Dinosaur Mailing List Archives. Retrieved 21 March 2010 (Named as Undescribed Carcharodontosaurine)